X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment8.mdwn;h=c954e955f249f5f3cf54c2f349ed2f710f962ea0;hp=abc14d08b87337bbaa56a1d025157714a0c6949a;hb=ad2f53317266fc3a57ba8dd05a0b90c55ef1d472;hpb=48a42d03d6e2562628e1ab9cc7e134cc9bcf4294 diff --git a/assignment8.mdwn b/assignment8.mdwn index abc14d08..c954e955 100644 --- a/assignment8.mdwn +++ b/assignment8.mdwn @@ -73,27 +73,34 @@ is equivalent to: (if (test1 argument argument) + ; then result1 + ; else (if (test2 argument argument) + ; then result2 + ; else (if (test3 argument argument) + ; then result3 + ; else result4))) Some other Scheme details: * `#t` is true and `#f` is false + * `(lambda () ...)` constructs a thunk + * there is no difference in meaning between `[...]` and `(...)`; we just sometimes use the square brackets for clarity * `'(1 . 2)` and `(cons 1 2)` are pairs (the same pair) * `(list)` and `'()` both evaluate to the empty list * `(null? lst)` tests whether `lst` is the empty list * non-empty lists are implemented as pairs whose second member is a list - * `'() '(1) '(1 2) '(1 2 3) are all lists - * `(list)` `(list1)` `(list 1 2)` `(list 1 2 3)` are the same lists - * `'(1 2 3)` and `(cons 1 '(2 3))` are pairs that are also lists (the same list) + * `'()` `'(1)` `'(1 2)` `'(1 2 3)` are all lists + * `(list)` `(list 1)` `(list 1 2)` `(list 1 2 3)` are the same lists as the preceding + * `'(1 2 3)` and `(cons 1 '(2 3))` are both pairs and lists (the same list) * `(pair? lst)` tests whether `lst` is a pair; if `lst` is a non-empty list, it will also pass this test; if `lst` fails this test, it may be because `lst` is the empty list, or because it's not a list or pair at all * `(car lst)` extracts the first member of a pair / head of a list * `(cdr lst)` extracts the second member of a pair / tail of a list - * `(lambda () ...)` constructs a thunk Here is the implementation: